Time delays in photoelectron emission are a highly sensitive probe of
the dynamics of electron ejection and subsequent scattering. Streaking [1]} and
RABITT [2]}, [3]} are two experimental techniques that can measure time delays
with resolutions on the scale of 10 as (1 as=\(10^{-18}s\) ). The high precision of these
measurements may uncover a variety of mechanisms that contribute to photoemission.
An interpretation in terms of “tunneling times”[4]} has created a long debate,
with recent measurements suggesting the absence of any such time delay in the tunnel process
[5]}.
The whole debate has also been hampered by serious conceptual questions related to the
definition and interpretation of any such delay time (see, for example,
[6]}, [7]}, [8]}, [9]}). In course of that debate,
awareness has been heightened that irrespective of delays that might be associated with the
photo absorption process, scattering delays dominate the measurements.
